The present invention pertains to a method of determining a working voltage of an inverter, which utilizes a rectifying method to transform an alternating current into a pulse direct current, and then via a working frequency, divides a direct current cycle, which ranges in a lowest voltage—highest voltage—lowest voltage manner, into multiple continuous voltage pulses. The inverter receives each one of the multiple continuous voltage pulses and acts in response to each one of the multiple continuous voltage pulses and corresponding to the voltage cycle ranging between the lowest voltage and the highest voltage to output a variable voltage signal to a load. Thus, the working voltage of the inverter is analogous to the input voltage of the alternating current, and a power-factor regulating effect can be accomplished directly by the inverter.